The present invention relates to an arrangement for the recognition of misfirings of a multi-cylinder internal combustion engine with externally controlled ignition, having a pair of thermo-elements connected with each other in opposite polarity, whereby one thermo-element each is arranged in an exhaust tract of two cylinders of the internal combustion engine and a threshold circuit detecting the resulting thermo-voltage at the free ends of the thermo-element pair produces a warning signal upon occurrence of a certain value of the thermo-voltage and/or interrupts a supply of operating fuel to the cylinders.
Especially with internal combustion engines having higher numbers of cylinders, it is frequently difficult to determine a misfiring of individual cylinders because these internal combustion engines then still exhibit a relatively great quietness (smooth running). However, this leads to a high exhaust of uncombusted fuel-air mixture, which burdens the environment or which may ignite explosion-like in the exhaust tract. In vehicles which are equipped with a catalyst, such uncombusted mixtures lead either to destructions of the catalyst carrier or to an overheating of the catalyst.
The U.S. Pat. No. 3,939,711 makes use of the fact that in case of failure of the ignition of a cylinder, the temperature of the gas mixture exhausted by the same drops. A thermo-element is therefore arranged in the exhaust tract of each cylinder of the internal combustion engine and all thermo-elements are connected in series coupled in opposite polarity. With an intact ignition, the thermo-voltages of all thermo-elements are equal so that with an even number of thermo-elements, they cancel one another. If an uneven number of cylinders fails or becomes inoperative, then a resulting voltage occurs at the free ends of the thermo-elements which rectified is utilized for the detection of the misfiring. However, it cannot be determined thereby which cylinders have misfired, i.e., only a global defection indication is possible thereby.
It is therefore the object of the present invention to provide a simple arrangement for the recognition of misfirings of multi-cylinder internal combustion engines which enables with simple means a selective recognition of misfirings of cylinders.
The underlying problems are solved according to the present invention in that the cylinders of the internal combustion engine are combined into groups having separate ignition circuits in a known manner and one thermo-element of the thermo-element pair is arranged in the exhaust tract of a respective cylinder of each group.
The advantages of the present invention reside in the first instance in that an arrangement is created which enables with simple means a selective recognition of cylinder misfirings. This permits, without damaging the exhaust system or the catalyst installation, to turn off the defective cylinders; an emergency operation of the internal combustion engine is therefore assured. Additionally, the defect diagnosis and the repair of the internal combustion engine is facilitated.